If you run Ant as a background process (like ant &)
and use the <java> task with spawn
set to false and fork
to true, you must provide explicit input to the forked
process or Ant will be suspended because it tries to read from the
standard input.

Parameters

Attribute

Description

Required

classname

the Java class to execute.

Either jar or classname

jar

the location of the jar file to execute (must have a
Main-Class entry in the manifest). Fork must be set to true if this option is selected.
See notes below for more details.

Either jar or classname

args

the arguments for the class that is
executed. deprecated, use nested <arg>
elements instead.

if enabled triggers the class execution in another VM
(disabled by default)

No

spawn

if enabled allows to start a process which will outlive ant.
Requires fork=true, and not compatible
with timeout, input, output, error, result attributes.
(disabled by default)

No

jvm

the command used to invoke the Java Virtual Machine,
default is 'java'. The command is resolved by java.lang.Runtime.exec().
Ignored if fork is disabled.

No

jvmargs

the arguments to pass to the forked VM (ignored
if fork is disabled). deprecated, use nested
<jvmarg> elements instead.

No

maxmemory

Max amount of memory to allocate to the forked VM
(ignored if fork is disabled)

No

failonerror

Stop the buildprocess if the command exits with a
returncode other than 0. Default is "false" (see note)

No

resultproperty

The name of a property in which the return code of the
command should be stored. Only of interest if failonerror=false
and if fork=true.

No

dir

The directory to invoke the VM in. (ignored if
fork is disabled)

No

output

Name of a file to which to write the output. If the error stream
is not also redirected to a file or property, it will appear in this output.

No

error

The file to which the standard error of the command should be
redirected.

No

logError

This attribute is used when you wish to see error output in Ant's
log and you are redirecting output to a file/property. The error
output will not be included in the output file/property. If you
redirect error with the "error" or "errorProperty"
attributes, this will have no effect.

No

append

Whether output and error files should be appended to or overwritten.
Defaults to false.

No

outputproperty

The name of a property in which the output of the
command should be stored. Unless the error stream is redirected to a separate
file or stream, this property will include the error output.

No

errorproperty

The name of a property in which the standard error of the
command should be stored.

No

input

A file from which the executed command's standard input
is taken. This attribute is mutually exclusive with the
inputstring attribute

No; default is to take standard input from console
(unless spawn="true")

inputstring

A string which serves as the input stream for the
executed command. This attribute is mutually exclusive with the
input attribute.

No; default is to take standard input from console
(unless spawn="true")

newenvironment

Do not propagate old environment when new
environment variables are specified. Default is "false"
(ignored if fork is disabled).

No

timeout

Stop the command if it doesn't finish within the
specified time (given in milliseconds). It is highly
recommended to use this feature only if fork is enabled.

No

clonevm

If set to true, then all system properties
and the bootclasspath of the forked Java Virtual Machine will be
the same as those of the Java VM running Ant. Default is
"false" (ignored if fork is disabled).
since Ant 1.7

No

Parameters specified as nested elements

arg and jvmarg

Use nested <arg> and <jvmarg>
elements to specify arguments for the Java class and the forked VM respectively.
See Command line arguments.

sysproperty

Use nested <sysproperty>
elements to specify system properties required by the class.
These properties will be made available to the VM during the execution
of the class (either ANT's VM or the forked VM). The attributes
for this element are the same as for environment
variables.

syspropertyset

You can specify a set of properties to be used as system properties
with syspropertysets.

since Ant 1.6.

classpath

Java's classpath attribute is a PATH like structure and can also be set via a nested
classpath element.

bootclasspath

The location of bootstrap class files can be specified using this
PATH like structure - will be ignored
if fork is not true or the target VM doesn't
support it (i.e. Java 1.1).

since Ant 1.6.

env

It is possible to specify environment variables to pass to the
forked VM via nested env elements. See the description in the
section about exec

Settings will be ignored if fork is disabled.

permissions

Security permissions can be revoked and granted during the execution of the
class via a nested permissions element. For more information please
see permissions

When the permission RuntimePermission exitVM has not been granted (or has
been revoked) the System.exit() call will be intercepted
and treated like indicated in failonerror.

Note:
If you do not specify permissions,
a set of default permissions will be added to your Java invocation to make
sure that the ant run will continue or terminated as indicated by
failonerror. All permissions not granted per default will be
checked by whatever security manager was already in place. exitVM will be
disallowed.

Settings will be ignored if fork is enabled.

since Ant 1.6.

assertions

You can control enablement of Java 1.4 assertions with an
<assertions>
subelement.

A nested I/O Redirector
can be specified. In general, the attributes of the redirector behave
as the corresponding attributes available at the task level. The most
notable peculiarity stems from the retention of the <java>
attributes for backwards compatibility. Any file mapping is done
using a null sourcefile; therefore not all
Mapper types will return
results. When no results are returned, redirection specifications
will fall back to the task level attributes. In practice this means that
defaults can be specified for input, output, and error output files.

By default the return code of a <java> is ignored.
Alternatively, you can set resultproperty to the name
of a property and have it assigned to the result code (barring immutability,
of course).
When you set failonerror="true", the only possible value for
resultproperty is 0. Any non-zero response is treated as an
error and would mean the build exits.

Similarly, if failonerror="false" and fork="false"
, then <java>must return 0 otherwise the build will
exit, as the class was run by the build JVM.

JAR file execution

The parameter of the jar attribute is of type File;
that is, the parameter is resolved to an absolute file relative to the
base directory of the project, not the directory in which the Java
task is run. If you need to locate a JAR file relative to the directory
the task will be run in, you need to explicitly create the full path
to the JAR file.

Run the JAR test.jar in this project's dist/lib directory.
using the manifest supplied entry point, forking (as required),
and with a maximum memory of 128MB. Any non zero return code breaks the build.